Medical electrodes are used to transmit electrical signals or currents between the body of a patient and external medical equipment. These electrodes typically include a conductive composition adhered to or otherwise in contact with, the skin of the patient, and a conductor, which is electrically connected to the conductive composition and to the external medical equipment.
Conventional conductive compositions include water containing hydrogels made from hydrophilic monomer solutions. Additives are commonly used to modify physical properties of conductive compositions resulting in compositions, such as hydrogels for use in medical electrodes, with uniform dimensions and performance properties. Polymeric thickeners have been used to increase the viscosity of monomer solutions, but may not prevent the solution from beading up on a hydrophobic surface (such as a film release liner) or lower the surface tension of the hydrophilic mixes. Polymeric thickeners usually require relatively high concentrations to achieve an effective viscosity and they tend to leave a residue after the monomer has been polymerized.
Surfactants have been used to lower the surface tension of the monomer mixes but they do not increase the viscosity. Moreover, even if the surfactant is added at relatively high levels, the monomer films are not dimensionally stable when coated on hydrophobic surfaces. Thus, conductive compositions for medical electrodes that are dimensionally stable on hydrophobic surfaces and that have uniform depth and performance properties may be desirable.